Physicists have been trying to use quantum mechanics for decades to build computers that could solve problems currently out of reach of classical machines. Options are many, including superconducting circuits, trapped ions, and semiconductor quantum dots. But now researchers are looking to a more unconventional candidate: electrons near the surface of superfluid helium.
Once seen as a physically quirky system, this is now emerging as a viable, scalable platform for charge- and spin-based quantum computing. Recently, Physics demonstrated that these electrons can strongly couple to microwave photons, enabling extremely precise quantum measurement and control. In more detail, the researchers achieved strong coupling between a microwave photon and the motional state of a single electron in superfluid helium.
A unique environment is provided by especially clean superfluid helium. It will flow frictionlessly at cryogenic temperatures over a defect-free liquid surface, where electrons can rise slightly below the surface. Stuck to the helium, those electrons are shielded against localized impurities that typically decohere other solid-state systems, making it an attractive platform for fragile quantum operations.
But isolation is not enough for computation. In a practical quantum processor, researchers need ways to read and adjust these electrons without obliterating their delicate quantum states. A formalism for it is provided by cavity quantum electrodynamics (cavity QED).
Scientists tested quantum electrodynamics more accurately than ever
A schematic representing cavity QED in which the interaction of a single electron and a single photon is enhanced by coupling it to a microwave resonator. Operating in the strong-coupling regime enables coherent transfer of information between matter and light, an essential ingredient for achieving distributed quantum computing.
This regime has already been used in superconducting qubits, atoms, and semiconductor quantum dots. Now, researchers have demonstrated it with electrons on helium, marking a major milestone.
The team built a device that combines a quantum dot that traps a single electron on helium with a superconducting microwave resonator. When the electron moved, its quantized motional state interacted with the resonator’s photons.
This resulted in a very tight coupling between the microwave photon and the motion of a single electron. Realizing this coupling on a helium platform provides the required first step in building spin qubit readout protocols. Spin–orbit hybridization techniques used in semiconductor quantum dots can now be realistically implemented on helium, enabling the realization of high-fidelity spin readouts for single electrons on helium.
Quantum electrodynamics proven to be 100 times more accurate than previous tests
Quantum computing in practice rests on fine manipulation and measurement of qubits. While cold atoms are promising qubit candidates, elegantly combining the isolation required for low-noise quantum processors and lithographic scalability, researchers find that electrons on helium combine the best ideas: they offer as truly small a hybrid system as an exceptionally low-noise environment (as well as up to three-dimensional confinement) while remaining a completely integrated multi-qubit controlled system with longer-range charge-correlated emission patterns.
Strong coupling shows that the quantum state of the electron can be probed and controlled very efficiently using microwave photons, paving the way for on-chip integration with future large-scale quantum networks that use light as an information carrier. This also suggests that he opens up the possibility of interfacing spin-based qubits on helium with existing superconducting quantum architectures.
This advancement goes beyond just providing a new platform for quantum computation; it offers a different physical system for studying the fundamental principles of quantum mechanics. The team uses quantum information science to develop superfluid helium in new regimes, and by bringing together the unique condensed-matter properties of superfluid helium with quantum information, an approach that optimizes researchers’ ability to investigate interacting electrons or photons or quantum dots in excellent experimental control, researchers are paving the way toward a future generation of transport experiments.
Subsequent experimental work will likely be needed to optimize these spin readout protocols and to extend this approach into arrays of helium-bound electrons configured in hybrid quantum circuits. Once these challenges are overcome, electrons on helium could provide an excellent architecture for a scalable quantum processor.
Quantum computing is often described as a “moonshot” technology, but progress is being made one careful experiment at a time. The demonstration of strong coupling between a photon and an electron on helium is more than a technical feat; it’s a glimpse of how diverse and creative the quantum revolution has become.
From superconducting circuits to trapped ions, and now to electrons floating on helium, the quantum future is being built on platforms as varied as the imagination of the scientists who design them.
Journal Reference:
- Koolstra, G., Glen, E.O., Beysengulov, N.R. et al. Strong coupling of a microwave photon to an electron on helium. Nat. Phys. (2026). DOI: 10.1038/s41567-026-03342-z
